The reason that 3rd parties don't work in the USA, but do work in a lot of other countries is that our constitution makes us vote directly for our president.
In England, Europe, Africa and South America almost every country just votes on their parliament (like we do our congress) and then the congress or parliament wheels and deals and elect (from within their ranks) the most acceptable Prime Minister or 'President' to us. So they don't vote for their top leader, they vote for their local representative. So, if they elect a Green Party candidate, a Jill Stein for ex. then she can put her support behind the most 'Green' President or Prime Minister available.
The USA constitution works differently.